Methods similar to that described above and programmed water-softening systems are known (German Laid-Open Application No. 16 42 525 as well as published functional drawings of Clearmaster Company). In this known process the regeneration medium is passed through the exchange medium with a flow speed of 3 to 5 meters/hour. Normally, during the slow rinse process, the flow is generally at the same speed, because the rinse is accomplished by the injected water by means of which the regeneration medium is being suctioned and circulated. The subsequent backflush is done at a speed of about 8 meters/hour, which is intended to accomplish a mixing of the exchange medium as well as the freeing and floating off of accumulated fine materials. In addition, the exchange medium is supposed to be loosened up by means of the circulation of the regeneration medium.
Furthermore, later and improved methods are known, where the regeneration process is first begun with a strong back-rinse process with a flow direction through the exchange medium from below to above and where the regeneration medium is then passed through the exchange medium in the opposite direction, i.e. from above to below, and where the rinse is accomplished slowly in the same flow direction as the regeneration medium. Finally, there is a fast rinse process with a flow direction from above to below. During the treatment process the untreated water enters from above and flows through the exchange medium to the bottom.
Additionally it is known to utilize either a timed or a metered flow control system with programmed water-softening systems. In timed control systems the timed interval between two regeneration cycles is pre-selected. The actual treated water use, therefore, is not taken into consideration; accordingly, a surplus capacity of the exchange medium, possibly still present at the time of the start of the regeneration process, is lost. This method is inefficient as a rule, because an amount of regeneration medium equivalent to the regeneration of a completely exhausted exchange medium has to be used for every regeneration cycle. At the other extreme it is possible that the exchange medium may be already exhausted before the end of the pre-selected time period for the next regeneration, so that the possibility of unwanted water hardness exists.
In the case of a metered flow control system the regeneration is triggered by the drawing off of a pre-selected amount of treated water since the last regeneration, which can be arrived at mathematically by taking the capacity of the water-softening system and the hardness of the untreated water into account and inserting this into the program. Systems of this kind are technically expensive and lead to long intervals between two regenerations, if little or no treated water is used over long periods of time. This leads to severe contamination of the exchange medium, which has to be avoided in certain areas, such as the domestic or the food handling sectors. Additionally, regeneration cycles can be triggered undesirably at just the time when the demand for water is high.